I know what you mean. My youngest is 1 next week. I also have a nearly 9 year old, a 4 year old and a nearly 3 year old. I think this time because she is definitely my last I am feeling it more than I did with the others. Each new milestone she reaches marks the end of an era. With the others there was always a chance that I would have another baby.
On the other hand I am also looking forward to the extra freedom that my babies growing up will give me